With the exception of ophthalmic lenses (which when mounted constitute spectacles, lorgnettes or the like of heading 90.04), this heading covers the articles referred to in Items (B), (C) and (D) of the Explanatory Note to heading 90.01 when in a permanent mounting (viz., fitted in a support or frame, etc.) suitable for fitting to an apparatus or instrument. The articles of the heading are mainly designed to be incorporated with other parts to form a specific instrument or part of an instrument. The heading does not include mounted optical elements which are in themselves separate appliances, for example, hand magnifying glasses (heading 90.13), and mirrors for medical or dental purposes (heading 90.18).
Subject to the above conditions, the heading includes :(1) Objective lenses, additional lenses, colour filters, viewfinders, etc., for photographic or cinematographic cameras or for projectors. (2) Polarising filters for microscopes or polarimeters. (3) Eyepieces and objectives (including polarising) for astronomical instruments, binoculars or refracting telescopes, microscopes, etc. (4) Mounted prisms for instruments or apparatus for physical or chemical analysis (polarimeters, etc.). (5) Mounted mirrors for telescopes, projectors, microscopes, medical or surgical instruments, etc. (6) Optical elements (lenses and prisms) for lighthouses or beacons, mounted on panels or drums. (7) Mounted lenses clearly identifiable as fittings for optical benches. (8) Mounted halftone or similar printing screens. The objective lens in an optical instrument is the lens system that faces the object, giving an image of the latter. It may be a single lens but is usually a group of lenses in a single mounting. Eyepieces are optical systems (placed near the eyes) through which a magnified image is observed. The heading does not cover : (a) Optical elements with a temporary mounting provided solely for protection during transport (heading 90.01). (b) Mounted glass mirrors, optically worked, which are unsuitable for fitting to instruments or apparatus (for example, certain rear-view mirrors, chimney or drain inspection mirrors, and special mirrors for wind-tunnel observations) (heading 90.13). (c) Sets of lenses put up in cases and designed for fitting into special frames for sight testing (used by opticians) (heading 90.18).
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